motor can act as an inductor?

[Tony Williams]

In article <7199d521.0402071429.e143995@posting.google.com>,
The Captain <Captain794@yahoo.com> wrote:

Tony Williams <tonyw@ledelec.demon.co.uk> wrote......
So I wonder if this characteristic is being used as an
'electrical flywheel', helping to smooth the terminal
voltage of the alternator.

It's been so many years since I studied this stuff, that I've
hesitated to contribute, but Alan's post rang a bell. If the
synchronous motor is swinging a large flywheel, then it seems to
me that it will act as an electrically coupled flywheel on the
driveshaft. If the shaft is driving a marine propellor which may
occasionally be raised out of the water by rough seas, then the
propellor will tend to run free with no torque on the shaft to
control engine speed. This will affect the power output of the
generator and, presumably, the frequency of the generated AC
current. With the electricaly coupled flywheel in place, the
shaft speed will be controlled by the back emf on the coupled
generator, safer for the mechanics and a method of controlling
the frequency of the generated power..

I'm not sure I'd go as far as suggesting that the
speed of the main engine could be stabilised. The
relative strengths, and sizes of the various elements
would seem to be too disproportionate.

I'll just stick with the original suggestion, that a
spinning induction motor takes/delivers large currents
in response to changes in the supply frequency (or the
voltage). In doing so it effectively reduces transient
voltage changes across the alternator's output terminals.

--
Tony Williams.

 

[Miles]

"The Captain" <Captain794@yahoo.com> wrote in message
news:7199d521.0402071400.78c2da29@posting.google.com...

JohanLexington@webmail.co.za (Johan Lexington) wrote in message
news:<d69e3ae6.0402030823.70d20768@posting.google.com>...
----
Actually, with all other things being equal, the stability limit of a
generator IS reduced at leading power factor because the excitation
voltage
is reduced and this affects the power transfer - look at the right
hand side
of the swing equation and what affects the transfer.
How do you think the right side of the equation was developed....MASS

Mass simply determines
how fast the machine swings. Also look at the steady state capability
limits
of a synchronous generator and steady state limitations (mass not
involved)
on leading operation. Paul is absolutely right.

Well, you are wrong also.

For motor operation, leading pf will be the overexcited case but for
generator operation it is the underexcited case. Suck the excitation
down
enough and the generator will fall out of synch below rated KVA.

Sorry, it's kVA. When you write things incorrectly more mistakes are
easier to understand.

This group is just too funny. I read it for the entertainment; not
the technical content.

The K in this case stands for Kilo, KVA being Kilo Volt Amps. Since
it is standard practice to write KV, KHz, etc, please explaine why, in
this particular case, a lower case k should be used.

If you read this group for entertainment, three questions arise:

1. Just how dull is your life? (Sorry guys, I know it's interesting
reading and writing in here, but there's a hell of a lot more to life
than this newsgroup!)

2. Why do you write to the group, providing no answers to
correspondents questions, and merely tell us how very, very clever you
are?

3. Just how insecure are you?

I don't normally get involved in these pissing matches, usually just
read and learn, but your attitude is obnoxious in the extreme and you
contribute nothing.

Cap.

The lower-case "k" ("kilo") is in fact correct. The raft of different
electrical and nonelectrical quantities, and the wide range of different
prefixes, means that they should be stated correctly to avoid being
misinterpreted or taken out of context - for instance kilowatt-hour is
kWh, not KWH - not that I've ever heard of a Kelvin-Watt-Henry ("KWH") but
it does illustrate the point that not stating units of measurement exactly
can lead to misinterpretations.

I too read the group (mostly) for entertainment, but there's no reason why
we shouldn't at least try to use correct terminology and measurements.

 

[Klaus Vestergaard Kragelu]

"John Woodgate" <jmw@jmwa.demon.contraspam.yuk> wrote in message
news:4W97jALFOWJAFwVY@jmwa.demon.co.uk...

I read in sci.electronics.design that The Captain <Captain794@yahoo.com
wrote (in <7199d521.0402071400.78c2da29@posting.google.com&gt about
'motor can act as an inductor?', on Sat, 7 Feb 2004:

The K in this case stands for Kilo, KVA being Kilo Volt Amps. Since it
is standard practice to write KV, KHz, etc,

But it ISN'T. The prefix for 'kilo' = 10^3 is 'k'. See IEC 60027-1. 'K'
is used, unofficially until quite recently, to mean 2^10 = 1024.

'K' isn't 2^10, but rarther Kelvin as in temperature.....

Cheers

Klaus

 

[John Woodgate]

I read in sci.electronics.design that Klaus Vestergaard Kragelund
<klauskvik@hotmail.com> wrote (in <402619e6$0$1615$edfadb0f@dread14.news
..tele.dk&gt about 'motor can act as an inductor?', on Sun, 8 Feb 2004:

"John Woodgate" <jmw@jmwa.demon.contraspam.yuk> wrote in message
news:4W97jALFOWJAFwVY@jmwa.demon.co.uk...
I read in sci.electronics.design that The Captain <Captain794@yahoo.com
wrote (in <7199d521.0402071400.78c2da29@posting.google.com&gt about
'motor can act as an inductor?', on Sat, 7 Feb 2004:

The K in this case stands for Kilo, KVA being Kilo Volt Amps. Since it
is standard practice to write KV, KHz, etc,

But it ISN'T. The prefix for 'kilo' = 10^3 is 'k'. See IEC 60027-1. 'K'
is used, unofficially until quite recently, to mean 2^10 = 1024.


'K' isn't 2^10, but rarther Kelvin as in temperature.....

No. There are two protocols. One for units and one for multipliers. It's

quite legitimate to write '2 KK' for a temperature difference of 2
kilokelvin. See ISO 7000 and IEC 60027-1.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

 

[The Captain]

Tony Williams <tonyw@ledelec.demon.co.uk> wrote in message news:<4c7d707580tonyw@ledelec.demon.co.uk>...

In article <7199d521.0402071429.e143995@posting.google.com>,
The Captain <Captain794@yahoo.com> wrote:

Tony Williams <tonyw@ledelec.demon.co.uk> wrote......
So I wonder if this characteristic is being used as an
'electrical flywheel', helping to smooth the terminal
voltage of the alternator.

It's been so many years since I studied this stuff, that I've
hesitated to contribute, but Alan's post rang a bell. If the
synchronous motor is swinging a large flywheel, then it seems to
me that it will act as an electrically coupled flywheel on the
driveshaft. If the shaft is driving a marine propellor which may
occasionally be raised out of the water by rough seas, then the
propellor will tend to run free with no torque on the shaft to
control engine speed. This will affect the power output of the
generator and, presumably, the frequency of the generated AC
current. With the electricaly coupled flywheel in place, the
shaft speed will be controlled by the back emf on the coupled
generator, safer for the mechanics and a method of controlling
the frequency of the generated power..

I'm not sure I'd go as far as suggesting that the
speed of the main engine could be stabilised. The
relative strengths, and sizes of the various elements
would seem to be too disproportionate.

I'll just stick with the original suggestion, that a
spinning induction motor takes/delivers large currents
in response to changes in the supply frequency (or the
voltage). In doing so it effectively reduces transient
voltage changes across the alternator's output terminals.

I guess it would depend on the relative sizes of engine and motor.
You're quite right about it reducing transiients. I believe power
companies use exactgly the same principle and have a freely spinning
motor hooked up to the power grid for the same purpose.

The inertia of the motor also tends to stabilize the frequency of the
grid. Mind you, it's a BIG motor.

Cap